I have been lurking in the forums for a while now, and I find that, overall, the quality of posts and discussion here are much better than the chum bucket of "open" forums.

The criteria might be arbitrary, but it is effectively the "price" you are paying to gain entrance into the discussion.  If you don't value the forum at a level to make 5 posts in the newb area, and browse for 4 hours, than you are unwilling to pay the (arbitrary or otherwise) required "cost" to gain posting privileges.

Keeping forums clean is a tough job, and better some simple filters than moderators being overburdened or the discussion being swallowed by spammers.